Field of technology

The invention concerns a depolymerization of the plastics, mainly mixtures of plastic materials from the municipal and industrial waste, where the process of depolymerization runs continually with high stability of the process values and resulting products, mainly its diesel and petrol fraction. The subject matter of the invention is a device for depolymerization of the plastic material with the continual insertion (filling) and removal of the material.

Prior state of the art

When processing the plastic material, mainly municipal and industral waste, a depolymerization and decomposition is used, whereby fission products are created, mainly in gas form, which subsequently condense in the distillation columns into the desired diesel and/or petrol fractions. During these processes it is necessary to achieve a stable depolymerization without the interruption of a whole cycle, which usually involves mechanical processing of the plastic material, its drying, degassing and subsequent heating in the reactor without the access of the air.

The solution according to the patent file SK 279397 B6 discloses a moving bed with a whirling motion of the solid particles which are exposed to intensive whirling. The mixing of the solid particles leads to problems with mechanical parts of the reactor and such a solution is suitable only for processing of liquid oil products or for processing of mixtures with liquid oil products.

Solutions according to EP 0591703 A2, EP 0687692 A1 , US 20170073584 A1 , WO 03104354 A1 , WO 9620254, US 5856599 disclose various complex systems and devices for depolymerization of the plastic material, mainly plastic waste. These systems and devices are complicated and require cyclical cleaning of the mechanical parts and produce low-quality resulting products.

Solution according to EP 2599854 A2 uses a group of vanes which at the same time move the processed material. The operation of this device is energetically very costly and only a low quality of resulting products is achieved.

Published file PL 355826 B1 discloses a system with a continuous removal of the heavy fraction in the lower part of the reactor; it does not disclose, however, how a stability and safety of the processes in the system - mainly in reactor - is achieved.

Publication WO2017116733 (A1) uses a feeder which operates as a gas-proof seal and it has a primary and secondary reactor, too; but it does not occupy itself with a method to regulate and stabilize the process of depolymerization. It has been proven during the operation of various devices for depolymerization of the plastic material, it is difficult to achieve, during the processing, a temperature stability and a temperature homogenity of the material in the reactor. The maintenance of the optimal temperature in a whole mass of the processed material in the reactor is, however, problematic under the operational conditions, since the continual process requires steady insertion of the plastic material and removal of a heavy fraction without stopping or cooling of the reactor. The technological devices used in this field usually stem from the general constructions within a chemical industry, which were not designed for processing of the plastic waste, where the processed material has low thermal conductivity and its heating leads to irregular temperature field. The known devices and methods cannot produce thermally homogenous environment in the pyrolysis reactor and because of this the thermo chemical processes are unrestrained. The resulting products are not homogenous even in cases of homogenous inputs, which requires their further processing and which raises the costs. In order to increase the capacity, the devices have large volume reactors where homogenous environment cannot be achieved.

Such solution is desired and not known which will stabilize the temperature - and therefore also chemical - processes, which will be reliable and suitable for the continuous operation.

Essence of the invention

The abovementioned deficiencies are significantly remedied by a method of thermic depolymerization of the plastic material, where the plastic material is first crushed and at least partly rid of moisture and then the plastic material is depolymerized in the reactor’s vessel without the access of the air and without the catalyst during at least partial mixing at temperature 200 °C to 500 °C, according to this invention which essence lies in the fact that the plastic material is lead to the reactor’s vessel through the feeder in the pre-heated and compressed state at temperature at least 150 °C, whereby the material is during the depolymerization taking place in the reactor’s vessel led to the vessel continuously with the volume or mass flow which is regulated in order to achieve a stable level and/or stable mass amount of the material in the reactor’s vessel.

The leading of plastic material into the reactor according to the proposed invention is a new step in processing of the plastic material, whereby it is not only a mechanical processing and moving of the plastic material, but the plastic material is plasticized already and at the increased temperature 150 to 200 °C a partial fission of the polymer chains takes place. The pressing of the plastic material is acompanied with a pushing of the air or other gasses, too, out of the crushed mass of the plastic material. Thanks to this the plastic material led on the entry of the reactor forms an air-tight seal (or cork, or stop), too. It is preferable if during the pressing of the plastic material in this phase a relative increase of the mass of the crushed plastic material takes place, which corresponds to the feed relative mass (relative weight) even to the value which approaches the material relative mas of the solid material in exactness of ±10%. Such pressing means that originally aerated mixture of the disintegrated particles of the platsic material is changed at the entry to the reactor to a solid mass, or mass flowing under the pressure out of the feeder, respectively the pressed platic material in the liquid or semiliquid form has a better thermal conductivity as the plastic material which is only crushed.

The term“continuously/continuous” in this text should be understood in the place of connection of the feeder to the reactor’s vessel and in the relation to the period of depolymerization. In short periods, in order of seconds, and at the level of the material in the reactor’s vessel, the process of addition of the plastic material can be discontinuous, since usually the perssed platic material falls from above, from the feeder’s outlet, whereby from the pressed flow a smaller clastuers of the plastic material are broken off and the fall on the level in the reactor’s vessel. It is impottant that the input of the plastic material per minute, and for a longer period, is regulated in such a way that gradually, after the depolymerization kicks off, a stable state between the approaching plastic material and the outgoing components is achieved, which is acompanied by the stabilization of the level of the material in the reactor’s vessel. The regulation of the level can be achieved by discontinuous addition of the plastic material, too, for example by addition of one does of a plastic material in a varying interval, which, however, leads to the undesired temperature fluctuation in the material in the reactor’s vessel and to lesser stability of the resulting products of depolymerization.

The task of the first stage (first phase) during depolymerization according to this invention is pressing of the crushed and at least partially dehumidified plastic material, whereby the plastic material is at the same time heated to 150°C. The plastic material is heated by the compression process itself which is accompanied by the friction and at the same time it is heated to the set temperature by the added heat, for example from the electric energy or burning of the gaseous fuel. At this processing outside the reactor’s vessel the mechanical-thermic processes of low-temperature depolymerization take place already, and at the same time the plastic material is homogenized and get rid of air. The heating of the plastic material in this phase of its pressing leads to better homogenity of the plastic material at the entry to the reactor. The pre-heating of the plastic material also lowers the temperature differences between the material already in the reactor and the added plastic material. The pressing of the plastic material to the state of the liquid or semiliquid matter, respectively, improves the conditions for heat transfer. In this file, this process is also called“first stage of processing”.

It is preferable if in the first stage of the processing a suction of the air and water vapors takes place at temperature where the depolymerization basically does not take place, yet, but the water is already vaporized, for example at temperatures ranging from 100°C to 130°C. The place of suction should not be connected directly with the reactor and it is thus preferable if the air and water vapors are sucked in the process of pressing and heating in the first stage, before the outflow of the plastic material to the reactor. It is preferrable if the place of suction is between the beginning and end of the pressing of the material; in case of the screw (threaded) extruder the place of suction should be in the middle thread of the length of the screw. In such case the pressed material at the end of the screw produces a gas-proof seal (or cork, or stpo) which prevents the connection of the suction with the entry to the reactor.

The place of the suction alongside the screw is chosen in such a way that in the place the plastic material is already sufficiently heated (above ca. 100°C) by gradual heating alongside the screw and at the same time so that pressed plastic material between the place of the suction and the inflow to the reactor creates a reliable gas-proof seal. In such chosen place of suction the temperature of the plastic material is less than 150°C and a suction of the liquid plastic material to the system of exhaustion does not take place.

For the pressing at the first stage of the processing the compression ratio will be at least 2:1 , preferably at least 3:1 ; the plastic material is exposed to pressure of 10 to 20 MPa (100 to 200 bar) and the increase of the plastic material alongside the screw is basically linear or, in the places of individual heating bodies, it proceeds in leaps, respectively.

In order to increase the stability and regulation of the process of the first stage of processing a method can involve a preparatory phase where the plastic material is crushed, homogenized and pre-heated. During the pre-heating the temperature of the plastic material can increase to 70 to 85 °C, which lowers the humidity. In the subsequent first stage of the processing the plastic material is pressed and heated, first to 100°C, when the water and humidity is vaporized. The water wapor and air which have been between the individual particles of the plastic material is in this phase sucked away by the vacuum air pump and the plastic material is basically without air and humidity subsequently pressed into a homogenous mass and heated to the temperature of 150°C. The preparation of the plastic material into the form which is rid of air and water and which is sufficiently homogenous has been proved as significant for the achievement of high and stable quality of the resulting products of depolymerization.

During the regulation of the flow of the added plastic material a height of the level of the material in the reactor’s vessel can be measured and/or measure a mass (weight) of the material which exits at the outlets of the reactor. The regulated and at the same time continuous addition of the pre-heated plastic material has a significant effect on the possibilities to achieve high stability of processes in the reactor. The depolymerization processes are to the large degree dependent on the temperature in a given place. Achieving the optimal temperature in a whole volume of the material in the reactor creates optimal conditions for the stable depolymerization with the resulting fractions in the desired scope. The stable level as well as stable mass of the material in the reactor is necessary to maintain during the process of depolymerization, whereby the resulting gas products at the same time leave from the reactor and in intervals or continually a heavy fraction is removed from the reactor.

The continuous inflow of the plastic material to the reactor ensures that the share of the plastic material flowing from the feeder (from the first stage) to the reactor (to the second stage) per, for example, one minute of the operation is just 3-5% of the overall volume of the material in the reactor.

The need for achievement of a stable level and/or stable mass amount of the material in the reactor’s vessel is related to the transfer of the heat from the heating source to the processed material. At stable level and/or stable mass amount of the material in the reactor it is easier to regulate the access of the heat to the reactor; the regulation is also more exact, At least partial mechanical mixing of the material in the reactor improves the transfer of the heat from the outer casing of the reactor to the mass of the processed material. Multiple features of the proposed invention through its mutual influence and also through synergetic effect lead to production of the homogenous temperature field in the mass of the material in the reactor. Thanks to the pressing and pre-heatiing of the plastic material a formation of a thin layer from polymers with low thermal conductivity is prevented in the reactor; such a layer would have caused as an isolation layer and would have caused increase of the temperature gradient. Thanks to such solution it suffices if the heat is led in through the casing of the reactor; it is not necessary for the heat exchange elements such as pipes and distributions systems, known in the prior state of the art, to interfere inside the reactor; where these heat exchange elements are present, they complicate the mixing of the material and cleaning of the reactor.

Thermic cracking (thermal cracking) in the reactor while the continual inflow of plastic of plastic material without significant temperature swings in the reactor ensures, together with the reduced pressure, that emergin gaseous elements quickly leave the reaction space, which limits the coure of the secondary reactions of gaseous hydrocarbons and hence the creation of coke, too.

The proposed invention is reliable in operation and the resulting petrol and diesel products are of such quality that they can be used as a fuel for combustion engines, for example, for cogeneration units producing electricity and heat. The invention ensures the stability of the process and offers means for effective control of the composition and quality of the resulting products.

The method according to this invetnion involves a measurement of the height of the level and/or the measuring of the mass of the material in the reactor, whereby the addition of plastic material is regulated pursuant to the changes in the height of the level and/or the changes in mass of the material in the reactor. This dependency can have operational inaccuracies related to the inaccuracy of the measurement, the dosage and the reaction times of individual subsystems; such inaccuracies will not be considered a deviation from the scope of this invention.

In order to achieve effective pressing and heating of the plastic material, it is preferable if the heat for the heating is added in the transporting, compressing and homogenizing stage, whereby the amount of heat in individual stages can be regulated independently. In the transport stage the crushed plastic material is transported to the zone of pressing. In the compression stage the plastic material is compressed and in the homogenization stage the plastic material, already in a semiliquid or liquid form, is mixed. All these stages can be realized within a single device in the screw extruder. The sucking of the air and water vapor is preferably placed within the compression stage.

In the reactor the material depolymerizes on the basis of thermic influnce from the heat added from the outside. In the reactor a fission of the long polymer chains to the shorter ones takes places; the polymer chains have mainly the form of n-alkanes, to a lesser extent isoalkanes, alkenes, cycloalkane and aromatics.

In order to achieve the stated goal of high stability and purity of the depolymerization it is preferable if the unevaporated heavier fractions and solid remnants are removed continuously from the reactor. Preferably it will be realized in the lower part of the reactor, where the heavy fraction and solid remnants will gravitationally leave the reactor through the opening to the post-reactor where the heavy fraction and solid remnants are dried at temperatures ranging from 500 to 800°C. The separation of this process from the post-reactor itself prevents the pollution of the products in the reactor. The term“post-reactor” denotes closed vessel which is connected to the outlets of the reactor (first reactor), whereby it can be also called“second reactor” or“dryer”.

The task of the post-reactor is to remove and process a material from the reactor which is no longer able to crack into gaseous elements at the temperatures in the reactor. The higher temperatures in the post-reactor lead to release of the gases and to production of dried solid remnants, which however can no longer pollute the main products lead from the reactor in the gaseous state. The transfer of the heavier fractions and solid elements from the reactor to the post-reactor is regulated by means of the valve on the outlet from the bottom of the reactor.

The deficiencies in the prior state of the art are also significantly remedied by the device for the thermic depolymerization of the plastic material which includes the closed vessel of the reactor to which a feeder for the input of the plastic material is connected and where the vessel of the reactoer has an ouput for the gaseous products of depolymerization; it has a mechanical mixer of the material and also an output on the removal of the unevaporated heavy fractions, according to this invention, whose essence lies in the fact that the feeder is adjusted for the pressing of the plastic material and for its continuous transfer to the reactor’s vessel, whereby the feeder is equipped by the heating of the plastic material and the feeder has a regulation of the flow of the outgoing plastic material, where the regulation of the flow is connected with the control unit.

In the preferable arrangement the feeder has a form of the screw extruder with the heated casing. The outlet of the screw extruder has a continuous character; the flow of the plastic material in the extruder’s head is continuous and it is simply regulated by the rotations (turns) of the screw. It is preferable of the heating in the feeder is ensured in various places, whereby at least one place of the heating is the compression zone where the plastic material is pushed to the walls of the extruder’s chamber, thanks to which a good transfer of the heat to the matter of the plastic material is ensured. In order to ensure sufficient compression of the entering plastic material and in order to achieve its mixing at the end of the screw, the screw has a changing cross-section and/or changing pitch of the thread. The extruder can have a conic head at the end, and on its outlet an increase of the speed of the flow of the plastic material in liquid or semiliquid state, respectively, happens.

With the solutions known in the state of the art the threaded conveyors are used as feeders of the material to the reactor. Such feeders are capable of continuous, uninterrupted supply of the plastic material into the reactor; however, knowledge and skills in the state of art do not put emphasis on the continuous supply of the material with the flow regulated pursuant to the level or amount of the material in the reactor. The feeder usually works in such a way that it worked with the same rotations and the flow per hour has been regulated by switching the feeder on and off, or the feeder worked uninterrupted but the plastic material has been inserted into the feeder’s hopper at certain intervals. In solution according to this invention the mass flow is regulated continuously and the plastic material is pre-heated.

The control unit of the device is connected with the sensor of the level of the material and/or with the measurement of the mass amount of the material in the reactor’s vessel. The device has many sensors during the operation, as well as regulatory and safety elements. Many of them are known in the prior state of the art; what is important is for achievement of the state technical tasks is continuous regulation of the material in the reactor.

The screw extruder with the heated casing in the preferable arrangement has a compression ratio at least 2: 1 , especially preferably 3: 1 and the place of suction of the air and water vapors is chosen in the middle third of the screw where the temperature of the plastic material ranges from 100°C to 130°C.

In order to achieve higher homogenity of the plastic material the device according to this invention involves a preparatory unit placed before the entry to the extruder. In the preparatory phase the plastic material is crushed and agglomerated. It is preferably if the plastic material in the preparatory unit is pre-heated to temperature 70 to 85°C, too, which lowers its humidity. A solution has proven preferable where the reactor involves a cylindrical double casing (double-coat, double-sheath) vessel with a conical bottom which is equipped with an opening connected with the post-reactor’s vessel. In the space between the outer and inner casing of the vessel a heating system is arranged. It is preferable if the heating system includes gas burners with multi-point heating which are placed in multiple places and the burning gases bather the inner casing of the vessel which leads to the passing of the heat on a large surface. The turbulent flux at the same time ensures a relatively equal heating of the reactor’s casing. The flues gases rise at least to the height in which the reactor is filled with the material and they leave the device through the upper outlet where they can be used as a secondary source of the heat. The use of the gas burners for the production of the heat is peferable also because after the processes are started its onw technological gas, which is produced as a by-product of the depolymerization, can be used for the heating of the reactor (and post-reactor, too).

In order to ensure simple construction as well as good thermal conditions of the depolymerization, the reactor’s vessel has a cylindrical shape ended by the conical tightening, where the radius of the cylindrical part is larger than the height of the level of the material in the reactor when measued from the bottom of the conical part. The mass of the material in the reactor thereby achieves outer delimitation which very roughly corresponds to the spherical cutting, which is the optimal shape for mixing as well as for equal distribution of the heat, and in this shape a relatively large surface from which the gaseous products of depolymerization are evaporated is achieved. Usually the level of the material in the reactor reaches one to two thirds of the height of the reactor’s vessel.

The main process of the depolymerization in the reactor takes place at least during partial mixing at the temperature 200°C to 500°C, preferably at temperature ranging from 350°C to 450°C and with pressure in the chamber being 15 to 40 mbar. In this file, this process is also termed as second stage of processing.

During the starting or restarting of the operation, that is, during the first start or when starting after the shutdown, it is preferable if the reactor is first filled by the oil which is then heated to the reaction temperature or at least to half the value of the reaction temperature, and only then is plastic material from the feeder moved to the reactor. The plastic material from the compression environment passes to the reactor where the pressure is preferably reduced.

The resulting lighter hydrocarbons are in the continuous regime led from the reactor through the cyclone separator to the return cooler (or reflux condenser). In the return cooler part of the hydrocarbons condenses on the basis of the chosen temperature in the cooler, and the reverse flow returns them back to the reactor which allows their further fission in the reactor. On the basis of the chosen temperature in the cooler a retention time in the reactor can be regulated and the main process can be thus optimalized from the point of view of the yield of the desired products. Behind the return cooler the hydrocarbon vapors pass to the condensation system where the processual gas is sparated as well as light petrol-water fraction, broad diesel fraction, and uncondensable gaseous fraction. The processes in the second stage of the processing are known in the prior art as partial processes; the sigificant benefit of the proposed invention is the achievement of the stable regulatory framework which achieves high purity and high quality of the resulting products.

The post-reactor, which is connected behind the reactor, will be preferably placed below the reactor so that the unevaporated heavier fractions and the solid remnants will gravitationally pass to the post-reactor without the need for pumping. The task of the post reactor is the ensure the removal of the solid remnants as the by-products of the depolymerization from the reactor, as well as their final gasification and drying, whereby the removal of such remnants from the reactor runs while the depolymerization in the reactor is still taking place; therefore, reactor needs not to be stopped and cooled. The post-reactor is connected to the reactor in such a way that the removal of the material is continuous from the point of view of the functioning of the reactor. A regulatory element is preferable used for regulation of the removal which alters the flow cross-section of the opening on the exit (outlet) from the reactor.

In order to achieve desired technical tasks according to this invention it is preferable if the plastic material is continuously added to the reactor and at the same time the unevaporated heavier fractions and solid remnants are continuously or at certain intervals removed while the reactor is active, whereby a stable level of the material or stable mass amount of the material is kept in the reactor, with the deviation not surpassing 30%, preferably remaining below 15%. A good result is achieved already with a solution where the plastic material is continuously added regardless of the method of the removal of the unevaporated heavier fractions and the solid remnants, or the good results are achieved when the unevaporated heavier fractions and solid remnants are removed continuously are at certain intervals with the reactor being active, reagrdless of the method of addition of the plastic material to the reactor. An arrangement is especially preferable where the addition of the plastic material as well as the removal of the unevaporated heavier fractions and solid remnants are both continuous, whereby both these processes are regulated in such a way that a stable level and/or the stable mass amount of the material in the reactor’s vessel is maintained.

The vessel of the post-reactor has its own heating, preferably in form of the gas burner which is supplied by the technological gas from the reactor after the initiation of the process in the reactor. Post-reactor can also have its own mixer. The gases rising from the post-reactor are getting rid of the impurities by the cyclone or the washing machine (washer). By the bottom of the post-reactor a threaded conveyor is placed which collects the solid remnants of the processing and moves then through the closable element to the atmospheric environment.

In order to regulate the flow of the material between the reactor and the post-reactor a sensor of the dynamics of the mixer in the reactor can be preferably used. The control unit assesses the resistance of the mixer; the increase of the resistance means that the vanes of the mixer at the given temperature move in the material with the change viscosity and/or density. In such state the mixing stops, changes its direction of mixing, opens a closable element at the bottom of the reactor and the material with the reverse movement of the mixing flows into the post-reactor. The time of opening and flowing of the material to the post reactor is regulated in such a way that the exactly set amount of material is transferred. Subsequently the reverse operation of the mixer stops, the outlet of the reactor is closed and the mixer operates normally. The mixer in the post-reactor operates during the whole process of the outletting of the solid particles from the reactor to the post-reactor.

If no further gasification of the dried material takes place in this post-reactor - which is manifested by the decrease in pressure - on the basis of the instructions from the control unit a conveyor is activated, for example threaded emptying device. The remnants are moved from the post-reactor to the closed container for the solid remnants, which has a form of the slag. The container is connected to the beck of the emptying conveyor by the quick connector. During the emptying of the post-reactor its mixer is active in the reverse motion. After the emptying the conveyor stops and the mixer enters into normal operation. The container for the solid remnants is sealed by the valve and after the disconnection of the quick connector it is transferred to the allocated space for the cooling of the solid remnants.

The stability of the process and the thermal homogenity is ensured during the process of drying of the solid remnants in the post-reactor, too, where the finalization of the processing of the entry raw material takes place. Heavy fractions are let to the post-reactor after the increase of the reasistance of the vanes mixing in this reactor, where the closable elements is opened and heavy fractions are let to the post-reactor where they are finally dried. After the set time the closable elements is once again closed. It is important that not whole volume of the reactor is let out, but only the heaviest elements which have sank to the bottom of the reactor.

The separation part of the device is usually composed of three distillation rectification filling columns. The product of the first column is a gaseous oil which passes through the pipe through the filtration and cooling system to the storage container. The product of the second and third column is a petro-water fraction which passes through the pipe to the reservoir tank with purging (sludging) equipment. After the purging this light fraction is passed through the pipes to the storage vessel (collection vessel) equipped by the recuperation of vapors. The output from the condensation system are gases, too, which have not condensated at the temperature 40°C. These gases are, after getting rid of the impurities in the absorber, led by the pipeline to the independent gas farm where they are processed and temporarily stored before use. The yield of the gas products ranges from 5 to 30% of the mass, the petrol fraction ragnes from 10 to 50% of the mass and the diesel fraction ranges from 20 to 85% of the mass. During the operation of the device it has been proven that it can handle a moderately polluted mixed plastic waste up to 10% of the mass without problems.

In order to achieve a compact construction of the device with low claims for space it is preferable if the device is placed within the frame construction whose outer dimensions match the dimensions of the transport container. Preferably the frame construction has connecting elements of the transport container, too, and it can be transferred and stacked as a common transport container. Such arrangement allows the device to be used as a mobile unit which is brought to the place of the plastic material dump.

A reliable removal of the humidity in the first stage of the processing has a positive effect on the course of the depolymerization; during the compression of the plastic material the air and the water vapor is sucked away. The continuous regulation of the amount and the entry temperature of the plastic material is important condition of the stability of the process. The achievement of the high stability and the reliable regulation ability brings about the possibility of continuous operation; it ensures low leve of pollution of the resulting products due to the fission of the solid shares. Thanks to the good manageability of the processes and fast regulation possibilities of the devices the yield of the individual fractions increases and pursuant to the current demands the quality and usability of all outputs can be managed. The stability of the processes without the sudden temperature shocks, mainly without cooling, achieves a homogenous product and lowers the risk of the creation of the dangerous and toxic compounds or toxic substances.

Description of drawings

The invention is further disclosed by help of drawings 1 to 8. The chosen ratio of sizes of individual elements of the device is illustrative only. The dimension ratios on the drawings cannot be interpreted as limiting the scope of protection.

Figure 1 displays a view of the connection of the feeder to the reactor. The thick arrows show the flow of the plastic material, its movement from the hopper with the shredder (grinder) to the extruder and subsequently to the reactor. The thin arrow in position 9 shows the suction of the air and water vapors from the extruder’s inside. For the sake of simplicity, the extruder in this drawing lacks the compress characteristic of the screw, even though in fact this, according to this invention, achieves the compression of the plastic material.

Figure 2 is a view of the extruder which in the direction of the flow of the plastic material has a transport zone, a compression zone and a homogenizing zone. For the sake of simplicity, the place of suction of the air and the water vapors from inside the extruder is not depicted in this figure. Figure 3 depicts the view of the reactor with the double-sheath (double-casing) vessel, where the outlet from the feeder is attached to the reactor from the above and the entry to the post-reactor is attached to the reactor’s bottom.

Figure 4 depicts the cooperation of the reactor with the postreactor, which has its own heating and mixing.

Figures 5 to 7 are views of the construction of the device placed in a compact cage with dimensions of two standardized containers. Figure 5 is a side view, the figure 6 is a front view from the side of the reactor, and the figure 6 is a bottom view.

A table pursuant to the figure 8 shows a course of the depolymerization pursuant to the temperature of the material in the reactor. Axis y marks the value of temperature in °C, axis x is time in hours.

Examples of realization

Example 1

In this example according to the figures 1 , 3 to 8 is a device with the necessary elements placed in the spatial frame construction which has an outer shape and dimensions of two standard transfer containers placed on each other.

The plastic material 4 is inserted to the hopper of the feeder 1 The feeder 1 in this example is formed by the screw extruder which has a similar construction as the pressing machine used when injecting the plastics in form of a granulate to moulds. The mixture plastic material 4 is crushed in the extruder’s grinder and thanks to the mechanical pressure connected with the thermic co-operation it is get rid of humidity. The crushed and degassed mixture plastic material 4 is moved in the closed cylinder of the extruder by a specially shaped screw which creates a compression zone 12.

The feeder 1 has a transport zone V\_ from which the plastic material 4 is moved to the compression zone 12 and where the plastic material 4 is pressed and runs in the pressed form to the homogenizing zone 13. Each zone V\_, 12, 13 is equipped with a heating 14 which transfers the heat through the feeder’s casing (sheath) to the plastic material 4. In the homogenizing zone 3 the plastic material 4 has a semiliquid form and it subsequently runs through the conical head of the feeder 1 and through the open spherical valve and with the temperature from 150°C to 200°C it falls from the upside to the reactor 2.

The plastic material 4 according to the figure 1 enters the feeder’s 1 hopper in part denoted as MF - entry of the plastic material 4. The humidity and dust is sucked by the fan from the feeder from above; these subsequently run through the condenser. Condensed humidity leaves from the chamber of the condenser in its bottom part. Air or offgas with dust, respectively, continue further to the dust filter; the purified air is then released to the environment through the exhaust head depicted in the left upper corner on figure 1. At the beginning of the process the plastic material 4 is crushed, dried and plastified, whereby a partial fission of the polymer chaines takes place in the feeder This stage can be called a first stage of the processing of the plastic material 4; the processing has a mechanical-thermiccharacter. In this example, the offgas from the grinder of the extruder according to the figure 1 is connected to the absorber with the vapors condenser, the vessel for the liquified gases and filter for the solid particles. The spread of the dust, impurities, gases and vapors from the grinder to the environment is thus ruled out.

Reactor 2 has a solid bed. The plastic material 4 is pre-prepared in the feeder which represents the first stage of the processing; it enters into the contact with the hot mass of the material 5 in the reactor 2 with temperature from 350°C to 450°C. The level of the material 5 in the reactor 2 ranges from one third to two thirds of the inner height of the reactor 2, whereby after the process runs on the stable level of the material 5 is maintained.

The reactor 2 has a cylindrical vessel with the conically shaped bottom, whereby it has a double-casing construction of the side part and the bottom. Inside, between the casings, is a heating 7 by means of the gas burners with a three pointed heating, who during the initiation use natural gas as a fuel G and after the initation of the depolymerization reaction they use their own technological gas which is produced as a by-product of depolymerization. The process in the reactor 2, as well as in the second stage, can be denoted as main stage and it runs with temperatures ranging from 350°C to 450°C. The ascent of flue gases from the heating 7 is depicted by the arrow marked EX.

The reactor 2 has a sensor of the height of the material 5; in this example it is an ultrasound distance meter placed in the upper part of the reactor 2 and oriented to the level of the material 5. The sensor is connected with the control unit which has a computer with programmed regimes and safety algorithms. The control unit is connected to the pressure sensors, temperature sensors and control of the individual regulation elements, motors, heating (gas burners) 7, heating 14 and other safety elements. The motor of the feeder 1 has continuously adjustable rotations in order to ensure the sufficient flow of the plastic material 4. The transitions between the feeder 1_ and the reactor 2, and the reactor 2 and the post-reactor 3, are equipped with the closable elements, by means of which a separation of the working spaces can be ensured if need arises, for example during initiation of the process or completion of the process. Similarly, the outlets from the reactor 2 and post-reactor 3 are equipped by the closable element.

The reactor 2 is equipped with the mechanical mixer 6. The depolymerization takes place during constant rotations of the mixer 6 and during stable pressure in the chamber ranging from 15 to 40 mbar. The resulting lighter hydrocarbons are in the continual regime led from the reactor 2 through the product pipe P and through the cyclone separator to the return cooler (reflux condenser). In the return cooler the condensing of the hydrocarbons happens on the basis of the desired temperature, and these are returned by the reverse flow to the reactor 2 which allows further fission in the reactor 2. On the basis of the desired temperature a retention time in the reactor can be set on the cooler; this optimalizes the main process from the point of view of yield of the desired products. Behind the return cooler the hydrocarbon vapors pass to the condensation system, where the processual gas, the light petrol-water fraction and broad diesel fraction as well as non-condensable gaseous fraction are separated.

Thermic cracking in the second stage with the continuous entry of the plastic material 4 to the reactor 2 ensured, and without significant temperature swings in the reactor 2, and at the same time during the reduced pressure, a state is achieved where the resulting gaseous components quickly leave the reaction space, which limits the course of secondary reactions in the gas hydrocarbons and thereby also the production of coke. The high temperature differences in the temperatures of the material 5 in the middle and by the reactor’s 2 walls also do not appear, which is important for the control of the temperature in the reactor 2 and also for the guidance and control of the quality and composition of the resulting products. The depolymerization has a stable course and it does not require a catalyst; it is ecological, and it does not produce new waste. The fission of the C-H bonds happens only under the influence of heat in combination with mechanical stress.

In the lower part of the reactor 2 is an opening followed by the entry to the post-reactor 3 which ensures the continual removal of the solid remnants as a by-product of the depolymerization from the reactor 2 and their final gassing and drying while the mass of the loose, powdery material composed from coke and mechanical purities is created.

The highest production of coke and the highest pollution of the liquid fractions happened in the stage of so-called drying. The separation, exclusion of the process of drying to the post-reactor 3, that is, the division of the whole process to the three phases which however take place continuously, ensures that the products of depolymerization are not polluted by the impurities - coke as well as decomposing products of the solid share. It is important that the flow of the plastic material 4, material 5 into the individual stages of processing, is continuous; the stopping of the reactor 2 is not required. The temperature in the post-reactor 3 ranges from 500°C to 800°C. An independent gas burner is used to heat the post-reactor 3. The secondary solid fuel from the own production of the device is used preferably as a fuel.

The post-reactor 3 has its own mechanical mixer and it has a conveyor 8 on its bottom for the collection of the solid particles which after the drying in the post-reactor 3 form the remnants SL not used during the depolymerization. The conveyor 8 has a closable element on its end in form of the controlled slider valve.

After the initiation to the operational state a quick temperature stabilization in the material 5 in the reactor 2 takes place; approximately after four hours the temperature is stabilized with the accuracy ± 10°C. The flow of the pressed plastic material at the entry to the reactor 2 in this example is ca. 7kg/min.

The device in this example is used for recyclation of the waste plastics which contain mainly polypropylene PP and polyethylene PE in any mutual ratio. The result of the process in this example is mainly a liquid fuel for the co-generation units which produce electric energy and heat. During the processing of the plastic material 4 which originates in the sorted municipal waste the process can be controlled in such a way that the yield of the gas products ranges from 5 to 30 % of the mass, the petrol fraction ranges from 10 to 50 % of the mass, and the diesel fraction ranges from 20 to 85 % of the mass.

The products can be used as an entry raw material for the operation of the petrochemical industry. The gaseous form of the resulting product includes heating gas for personal use for the development of the necessary processual heat as well as for other energetical purposes.

Example 2

In this example the feeder 1 pursuant to the figure 2 has a screw with a shifting geometry to ensure the desired compression ratio 3:1. The casing of the feeder 1 has, aside from the electric heating 14, gas burners, too, which are supplied by the technological gas from the reservoir.

The plastic material 4, pre-processed in the first stage, that is, in the feeder 1 is moved to the reactor 2 - whih is the second stage - not in batches, like in the cases of devices known in the prior state of the art, but by flow, that is, by continuous and regulated rotation of the feeder’s 1 screw. The plastic material 4 during this process continuously flows into the space of the reactor 2, where there is a mass of the material 5 heated to the reaction temperature. Less than 5% of the overall mass of the material 5 in the reactor 2 is thus transferred to the reactor 2 per minute.

After the device is started and after each shut down at least 200 litres of oil is placed into the cold reactor 2 and after its heating to at least half the reaction temperature the plastic material 4 starts to move to the prepared reactor 2 from the feeder 1 With such initiation there are no temperature shocks or decrease of the temperature in the reactor 2. The melt of the plastic material 4 which flows from the first stage to the second stage in the reactor is quickly heated after the contact with the hot reaction mass of the material 5 in the reactor 2, thanks to its previous preparation, too, and thermo-chemical destruction occurs.

The course of the temperature in the mass of the material 5 and the activity of the feeder is captured in the following table: _

The oil is heated in the reactor 2 to the temperature 200°C. From 1 :36 to 3:18 the initiation of the device ran during the continuous flow of the melt of the plastic material 4, heated to ca. 150°C. From 3:18 to 3:57 the flow of the melt of the plastic material 4 was stopped in order to achieve faster initiation of the temperature. Then the flow of the melt of the plastic material 4 was once again started and the device ran in the stable regime for next 2 days, whereby the reaction temperature was 400°C ±10°C.

Example 3

A plastic material 4 enters the feeder through a preparatory unit where the plastic material 4 is cut and subsequently neated to ca. 80°C. At this temperature the drying of the plastic material 4 takes place, the water vapor leaves through the ventilation chimney from the preparatory unit. The complete removal of the chemical unbound water and surface humidity from the particles of the plastic material 4 takes place during processing in the feeder 1

The feeder 1_ according to figure has a screw with the compression ratio 3: 1. Within the compression zone 2 an opening for suction 9 is produced in the feeder’s casing. The suction 9 is at a place where the plastic material 4 in the feeder has a temperature surpassing 100°C, but the plastic material 4 in this part of the feeder remains still in the particle, non-liquid phase, whereby the air and water vapor which is present between the separate particles of the plastic material 4 can flow into suction 9. Subsequently the plastic material 4 is pressed into the compact form and it runs semiliquid, at temperature ca. 180°C, from the outlet of the feeder through the safety reverse valve to the reactor 2.

The plastic material 4 in the preparatory unit and then in feeder is processed continuously, whereby the individual process run at suitable fringe conditions, not together in a common space. First the plastic material 4 is milled, cut or otherwise particularized so that better approach to the surface of the individual particles is achieved; the plastic material 4 is dried firstly at lower temperature, then it is pressed while continuously heated, and after the temperature rises above 100°C an air, water vapors or other easily suckable substances are sucked from the mass of the plastic material 4. Subsequently the plastic material 4 is pressed into semiliquid or liquid phase and its temperature is increased just below the threshold of the depolymerization temperature. Such prepared plasitc material 4 at the entry to the reactor 2 does not produce leap changes in temperatory and changes of homogenity in the reactor 2. This, together with the continuous dosage of the entering plastic material 4, brings about the stability of the resulting products of depolymerization.

The yield of the gas products ranges from 5 to 30 % of the mass. The yield of the petrol fraction ranges from 10 to 50 % of the mass. The yield of the diesel fraction ranges from 20 to 85 % of the mass.

Industrial applicability

The industrial applicability is obvious. According to this invention it is possible to industrially and repeatedly depolymerize plastics, mainly mixed plastic material from the municipal and/or industrial waste and also produce and compose a device for depolymerization. The results are mainly liquid products usable as a secondary fuel in cogeneration units or usable for processing in further processes during production of other chemical products.

List of symbols and positions

1- feeder

11 - transport zone

12 - compression zone

13 - homogenization zone

14 - heating

2- reactor

3- post-reactor

4- plastic material

5- material 6- mixer

7- heating (gas burners)

8- conveyor

9- suction

MF - material feed

EX - exhaust

G - gas

P - product

SL - slag (unused solid particles)